1. Field of the Invention
This invention relates to material mixing or blender devices for use in various industries, and more particularly to such apparatus as intended for use in solid-solids or liquid-solids blending operations. More specifically, the present invention relates to a novel agitator or intensifier.
2. Description of the Prior Art
In the prior art, various type mixers or blenders have been developed for use in blending solid-solids or liquids-solids to achieve dry or wet blends of materials. These prior art mixers and blenders have comprised variously shaped tumbler devices with or without internal baffles, agitators, intensifiers or the like and as liquid dispersion or attrition bars.
One such prior art blender is known as a cone or double cone blender. This blender derives its name from its shape and comprises a vertical cylinder with conical ends which rotate about a horizontal axis. The double cone blender suffers from the disadvantage of symmetrical flow pattern with maximum flow at the center. This tends to fill the space mostly from the middle, leaving the material near the trunnion relatively unmixed. Consequently, excessively long mixing periods are required for blending because of poor axial flow of materials.
Another form of solid-solids blender known in the art is a ribbon blender. Such blender comprises a stationary trough-type shell fitted with longitudinal shaft on which are mounted arms supporting slender spiral ribbons. It is one of the oldest mechanical mixing devices used for solid-solids mixing. This blender is effectively used for low-density solids, materials that aerate readily and light pastes. It is not recommended for precision blending, abrasive materials, material that packs, or when frequent cleaning is required. It is also not suitable for dense materials because of excessive power requirements. Unmixed material tends to accumulate at ends and at shell wall because of blade clearance. Ribbon blenders also suffer from the disadvantage of poor axial flow of materials.
Still another form of blender is my blender developed in the late 1940's and patented July 4, 1950, under U.S. Pat. No. 2,514,126, herewith incorporated by reference. This blender comprises two opposed simple cylinders formed into a "V". An outgrowth of the simple cylinder, the dual shell blender overcomes discharge problems and creates additional mixing action at the center. This extra action is responsible for faster, more efficient blending action than produced by a single cylinder and relies for its primary mixing action on intermeshing of solids at the center line.
A modification of the above-noted patent includes an agitator or intensifier as is disclosed in U.S. Pat. No. 2,677,534, issued May 4, 1954. As described therein, the agitator is turned at a very high rate of speed relative to the rotation speed of the blender itself and, thereby, effects dispersion of the materials within the blender.
In a further improvement of the dual shell blender with intensifier, the intensifier may include channel outlets through which liquid may be dispersed into the blender. Such an arrangement is shown for example in the publication "Patterns of Precision in Processing Equipment", copyright 1976 by Patterson Kelly Co., a division of Harsco Corporation and assignee of the present invention. Use of such a liquid adding intensifier provides a convenient technique for blending liquids and solids. The use of such liquid dispersion intensifiers is also disclosed in my U.S. Pat. No. 2,890,027, issued June 9, 1959, U.S. Pat. No. 3,362,688, issued Jan. 9, 1968 and U.S. Pat. No. 3,635,443 issued Jan. 18, 1972, which patents are herewith incorporated by reference.
Another patented improvement to the basic dual shell blender is disclosed in my aforesaid U.S. Pat. No. 4,141,657, issued Feb. 27, 1979. That patent discloses a modified dual shell blender wherein one of the legs has a different length than the other leg. Such disparity in the lengths of the legs was found to produce a surprisingly synergistic action which dramatically reduced the mixing time over that normally experienced with dual shell blenders having legs of the same length.
As previously noted, the use of liquid dispersion intensifiers with blenders is known to the art. Such intensifiers may include a plurality of canted disc assemblies, at least one disc assembly located in each of the moving chambers of the blender. The canted disc assemblies have dispersion blades and the intensifier is disposed such that the slant in each disc is asymmetric with respect to the axis of intensifier rotation i.e. each point on the circumference of the disc will not be tracking the point 180.degree. around on the circumference, but instead will be aerating an area axially removed within the blender. Because each point on the circumference of the canted disc is aerating or "plowing through" an area different from the other circumferential points, more power is required than would otherwise be the case. Furthermore, this asymmetry of the canted disc design makes great care and precision necessary in balancing the intensifier. Additionally, the use of a plurality of disc assemblies requires a complicated and costly shaft construction to ensure equal liquid flow patterns through each disc assembly.
In contrast to the relatively high power required for driving a canted disc intensifier, an intensifier which is symmetric with respect to the axis of rotation will require low power. Such an intensifier construction is shown in the above mentioned U.S. Pat. Nos. 2,677,534 and 3,635,443 wherein the intensifier is symmetric with respect to the axis of rotation. Each circumferential point on the intensifier shaft and on each one of paddles follows in the path of rotation of at least one other point on the intensifier. Accordingly, less power is required than for the asymmetric intensifier arrangement; However, the symmetric intensifier arrangement tends to throw material directly radially outward. This is disadvantageous because it tends to impede the flow of material from one leg to the other leg.
While the addition of liquid dispersion intensifiers into dual shell blenders provides a generally efficient method of combining liquids and solids, the use of a symmetrical high intensifier is disadvantageous since it tends to work against the desirable flow of materials from one leg of the blender to the other leg. On the other hand, where a canted disc assembly or other asymmetric intensifier does not adversely affect the cross flow of materials as much as a symmetrical intensifier does, such an intensifier consumes greater amounts of power and requires more precision in balancing than a symmetrical intensifier. Both of the latter types of intensifier also require placement of individual disc assemblies in each shell.